Slide fasteners

ABSTRACT

A slide fastener has a coating of waterproof plastics material formed by extrusion onto the closed fastener. The slide fastener comprises two woven elongate stringers, each having a series of spaced locking members which interlock when the fastener is closed, and coating which encloses the fastener and includes a longitudinally slit projection formed on each side of the locking members. The fastener has improved waterproofing as the fastener is fully enclosed by the plastics material when it is closed, and the plastics material moulds itself round both sides of the locking members.  
     To be accompanied, when published, by FIG.  1  of the drawings.

[0001] This invention relates to waterproof slide fasteners.

[0002] Slide fasteners, commonly known as zips, are used to fasten two flexible members releasably, usually at or near their edges. The slide fastener has two flexible elongate stringers, each of which have a series of spaced locking members like teeth, which interlock when the fastener is closed. Zips have many uses, for example in fastening clothes, tent flaps, bags and the like. However, ordinary zips are not waterproof, as there are gaps between the locking members, and the stringers are usually of woven cloth.

[0003] There are several waterproof zips known, but they tend to be very expensive because they are difficult to manufacture. The most expensive has stringers of plastics material, and two separate sets of interlocking teeth, separated by a sealing member. Another, less expensive, zip has woven stringers and a plastics coating moulded over one side including a projection over the teeth, the projection being slit longitudinally to allow the zip to open and close. On the other side of the zip there is only a thin covering of plastics over the teeth which can allow moisture through if the closed zip is flexed so as to open up the slit in the projection. The uncoated side of the woven stringers can also allow moisture to penetrate. The moulding process used for the plastics is relatively slow as it is time-consuming to set each zip up in the machinery.

[0004] According to a first aspect of the present invention, a slide fastener having two woven elongate stringers each having a series of spaced locking members which interlock when the fastener is closed, has a coating of waterproof plastics material formed by extrusion onto the closed fastener, the coating enclosing the fastener and including a longitudinally slit projection formed on each side of the locking members.

[0005] The waterproofing of the fastener is improved as the fastener is fully enclosed by the plastics material when it is closed, and the plastics material moulds itself round both sides of the teeth. Providing the projections on each side of the teeth means that if the fastener is flexed so that one slit opens up, the other slit is compressed to seal more firmly. Coating the fastener by extrusion is versatile, as it enables fasteners of different lengths to be processed easily

[0006] With the fastener flat, the edges of the projections separated by the slit will normally be in abutment, so that they provide an adequate seal. If a more positive sealing engagement is required, at least one of the edges of a projection may be biassed towards the other one.

[0007] The slide fastener may be of any conventional kind, where the locking members on each stringer are separate, or formed from a cut spiral member.

[0008] The extrusion coating process is performed by pulling a closed fastener through a cross-head extrusion die. The plastics material is allowed to cool, and then the slits in the projections are formed by putting the fastener through a slitting tool. If the sealing engagement is to be enhanced, at least one edge of a projection is heated locally, and then has pressure applied to it to produce the biassing.

[0009] The waterproof plastics material is preferably a high performance polyester such as Dupont's Hytrel (RTM), but may be any other suitable material, such as a polyurethane.

[0010] The invention also relates to a method of making a waterproof slide fastener.

[0011] According to a second aspect of the invention, a method of making a waterproof slide fastener comprises the steps of:

[0012] taking a closed slide fastener having two woven elongate stringers, each having a series of spaced locking members which interlock when the fastener is closed;

[0013] feeding the fastener through an extruder for plastics material;

[0014] extruding a coating of waterproof plastics material to enclose the fastener and to provide a projection on each side of the locking members;

[0015] allowing the coating to cool; and

[0016] slitting each projection longitudinally

[0017] The step of slitting each projection is preferably performed by passing the coated fastener through a slitting tool.

[0018] The method may include the further step of heating an edge of the top surface of a projection adjacent the slit, and applying pressure to the heated surface to bias the edge towards the slit. The pressure may be applied by a roller.

[0019] Embodiments of both aspects of the invention are illustrated by way of example in the accompanying drawings, in which;

[0020]FIG. 1 is a plan view, part cut away, of a slide fastener according to the first aspect of the invention;

[0021]FIG. 2 is a cross-section on the line 2-2 of FIG. 1; and

[0022]FIG. 3 shows a scheme of apparatus for performing the method according to the second aspect of the invention.

[0023]FIGS. 1 and 2 show a waterproof slide fastener 1. The fastener 1 comprises two elongate stringers 2, 3 of woven material, each stringer 2, 3 having a series of spaced locking members in the form of teeth 4, which interlock when the fastener 1 is closed. The stringers 2, 3 and teeth 4 have an extruded coating 5 of waterproof plastics material, the coating 5 enclosing the whole fastener, extending beyond the stringers 2, 3 and including a longitudinally slit projection 6, 7 formed on each side of the locking teeth 4.

[0024] The slit 8 in each projection 6, 7 enables the fastener 1 to be opened and closed by means of a conventional slider (not shown). The adjacent edges 9, 10 of each slit 8 abut when the fastener 1 is closed and flat, to provide a seal against moisture. If the fastener 1 is twisted or flexed so as to open up one of the slits 8, the other slit 8 will be compressed, thus ensuring that a seal is maintained. Extrusion of the coating 5 ensures that the plastics material fills the gaps between the teeth, which also helps with the sealing properties of the projections 6, 7.

[0025] The waterproof plastics may for example be Dupont's Hytrel (RTM), a polyester, or a polyurethane or the like.

[0026] The fastener 1 is made using the apparatus shown schematically in FIG. 3. FIG. 3 shows a cross-head extruder 11, and a slitting tool 12 having two opposed cutting blades 13. A slide fastener 1 of conventional construction, with the two stringers 2, 3 having locking teeth 4 is pulled through the die of the extruder 11, which applies the plastics coating 5, including the projections 6, 7 which are formed without the slits 8. The plastics material is allowed to cool and harden, and is then passed through the slitting tool 12, where the cutting blades 13 cut the slits 8 in each projection 6, 7.

[0027] In a modification, a further processing step is carried out following the slitting tool 8. to enhance the seal between abutting edges of each slit 8. This step is carried out by a heating and pressure-applying tool 14, through which the fastener 1 passes. The tool 14 firstly heats the top surface of each projection 6, 7 at at least one edge of each slit 8 and then applies pressure to the heated edge by a roller 15, to deform the edge slightly, biassing it towards the other edge. After passing through the tool 14 the fastener 1 is allowed to cool, and the deformed edge provides an enhanced seal for the slit 8.

[0028] It will be appreciated that the slider used to open and close the fastener, and any end stops for it will also need to be waterproofed.

[0029] In the embodiment illustrated the locking teeth 4 are separate members crimped or moulded into an edge of each stringer 2, 3. It is also known for the locking members to be formed from a spiral member, and fasteners with this type of locking member can also be waterproofed in accordance with the invention.

[0030] The slide fastener according to the invention is particularly useful for tents, as well as clothes and bags that need to be waterproof. 

1. A slide fastener having two woven elongate stringers, each of said woven elongate stringers having a series of spaced locking members, therein said series of spaced locking members interlock when said fastener is closed, said fastener having a coating of waterproof plastics material, said coating being formed by extrusion onto said fastener when said fastener is closed, said coating enclosing said fastener and said coating including a longitudinally slit projection formed on each side of said locking members.
 2. A slide fastener according to claim 1, wherein each of said longitudinally slit projections has two edges on opposite sides of said longitudinal slit in said projection and at least one of said edges of one of said longitudinally slit projections is biassed towards the other edge of said projection.
 3. A slide fastener according to claim 1 wherein said coating is applied by pulling said fastener through a cross-head extrusion die when said fastener is closed.
 4. A slide fastener according to claim 3, wherein each of said slits in said projections is formed by putting said fastener through a slitting tool.
 5. A slide fastener according to claim 2, wherein each of said slits in said projections is formed by putting said fastener through a slitting tool and at least one edge of one of said projections is heated locally and subsequently subjected to pressure to produce said biassing.
 6. A method of making a waterproof slide fastener, comprising the steps of: taking a slide fastener having two woven elongate stringers, each of said stringers having a series of spaced locking members, said series of locking members interlocking when said fastener is closed and said series of spaced locking members having an upper side and a lower side; feeding said fastener when said fastener is closed through an extruder for plastics material; extruding a coating of waterproof plastics material onto said fastener to enclose said fastener and to provide a projection said upper side and said lower side of said locking members; allowing said coating to cool; and slitting each of said projections longitudinally to provide each of said projections with a slit and two edges adjacent said slit, said edges being on opposite sides of said slit.
 7. A method according to claim 6 wherein said step of slitting each of said projections is performed by passing said coated fastener through a slitting tool.
 8. A method according to claim 6 wherein said method includes the further step of heating at least one of said edges of at least one of said projections adjacent said slit of said projection, and applying pressure to said edge that has been heated to bias said edge towards said slit.
 9. A method according to claim 8, wherein said pressure is applied to said edge that has been heated by a roller. 